in the process known as facilitated diffusion a special carrier protein with a central Channel acts as a selective Corridor which helps molecules move across the membrane these special carrier molecules that form the protein Channel bind only to a specific molecule such as a particular sugar or amino acid once the molecule binds to the carrier protein this protein helps or facilitates the diffusion process by changing shape and moving the molecule down its concentration gradient through the membrane into the cell where it is released facilitated diffusion is similar to simple diffusion in that both involve movement of molecules down their concentration gradient and this movement is carried out without any input of energy however in facilitated diffusion the movement of molecules will only take place if it is facilitated or helped by a special protein carrier in the membrane facilitated diffusion can occur in either direction depending on the concentration gradient if there is a higher concentration of the particular molecule inside the cell the same carrier protein would then transport the molecules out of the cell